1. Field of the Invention
The present invention relates to a disc driving device and particularly to an improvement of a housing of a disc driving device.
2. Description of the Prior Art
FIG. 3 is an exploded perspective view showing a carriage assembly and a housing in a conventional disc driving device.
In the same figure, the reference numeral 1 denotes a carriage assembly. The carriage assembly 1 is generally constituted by connecting through a hinge portion 6 a carriage 2 which carries thereon a lower magnetic head 4 and an arm 3 which holds an upper magnetic head 5. The arm 3 is capable of being opened and closed in the direction of arrow A relative to the carriage 2. In place of the upper magnetic head 5, a pad may be attached to the arm 3. Numerals 7 and 8 denote first and second guide shafts, respectively. The guide shafts 7 and 8 are slidably inserted into the carriage 2 and fixed to a later-described housing 9. By the use of a stepping motor (not shown) and a screw shaft which is driven by the motor, the carriage assembly 1 is moved in the direction of arrow B, namely, in a radial direction of a disc, while being guided by the paired guide shafts 7 and 8.
In the housing 9 is formed a disc driving motor mounting hole 10. Moreover, a pair of front bearing portions 11a and 12a are positioned near the mounting hole 10, and a pair of rear bearing portions 11b and 12b are formed in positions spaced by predetermined distances from the front bearing portions 11a and 12a. The front bearing portion 11a and a rear bearing portion 11b which are located in opposed positions constitute a first bearing portion 11 to support both end portions of the first guide shaft 7. Likewise, the front bearing portion 12a and the rear bearing portion 12b constitute a second bearing portion 12 to support both end portions of the second guide shaft 8. More specifically, both end portions of the first guide shaft 7 and those of the second guide shaft 8 are fixed onto the first and second bearing portions 11 and 12, respectively, by fixing shaft pressing pieces 13, 14 and 15 with bolts in the directions of P, Q and R as shown in the figure.
When the disc is placed on a turntable which is driven by a disc driving motor (not shown), and is rotated in a predetermined fashion, the carriage assembly 1 is moved in the direction of arrow B, namely, in a radial direction of the disc, with the disc held between the upper and lower magnetic heads 5 and 4, to effect a desired recording or reproducing operation.
The housing in such disc driving device has a predetermined shape obtained by a secondary machining after die casting from an aluminum alloy, for example. During this secondary machining, the first and second bearing portions 11 and 22 are formed accurately using a cutting tool. At this time, if the machining accuracy of the bearing portions 11 and 12 is not sufficiently high, there may arise an error in the contact pressure between the upper and lower magnetic heads 4, 5 and a recording surface of the disc, or a movement error exceeding a predetermined amount, which would exert a bad influence on the product performance.
However, the construction of the housing 9 in the conventional disc driving device requires a cutting tool to be moved along an underside path when shifting the cutting tool from one bearing portion 11 (or 12) to the other bearing portion 12 (or 11) in the secondary machining, thus resulting in deterioration of the machining accuracy or increase of the machining time. More particularly, when effecting a cutting operation from the first bearing portion 11a to the second bearing portion 11b, it is necessary to follow such a path as shown in a schematic plan view of FIG. 1 in which a cutting tool is moved horizontally from the front bearing portion 11a to the rear bearing portion 11b, then once raised, thereafter brought down into the rear bearing portion 12b of the second bearing portion 12, and then moved horizontally up to the front bearing portion 12a. such ascending and descending motions (indicated by broken line arrows in the figure) of the cutting tool involve backlash, so the machining accuracy is deteriorated; besides, the operation becomes more complicated, causing an increased working time. As an alternative route, after completion of the cutting operation for the first bearing portion 11, the cutting tool is moved back from the rear bearing portion 11b and moved horizontally to the second bearing portion 12. In this case, however, the degree of area will turn worse markedly because of re-cutting of an already cut face.